Scientists at the Natural History Museum, UK, have discovered that a strange knob-like ball on the wings of an extinct bird species called the Rodrigues Solitaire was a deadly weapon, used by the bird to defend territory and its mate.

Restoration of the Rodrigues Solitaire, a flightless member of the pigeon order endemic to Rodrigues, Mauritius (Frederick William Frohawk, 1907)

The Rodrigues Solitaire (Pezophaps solitaria) was a giant flightless pigeon that, like its closest relative the dodo (Raphus cucullatus), became extinct soon after European explorers settled in its habitat. It had a knob-like ball on its wings and although it was known to be aggressive, it was unclear what this structure was for, until now.

Dr Julian Hume and Dr Lorna Steel studied records from the 18th and 19th centuries, when many detailed studies were written by Europeans explorers in Rodrigues, on the Mascarene Islands in the Indian Ocean. They also analyzed in microscopic detail the ball structures on fossil solitaire bones.

They found that the so called ‘musket ball’ was indeed a weapon and that it was not found in any other bird. The largest they uncovered grew to 1.3 inches (3.3 cm), nearly as large as a ping-pong ball.

“There were even reports that it made a sound like thunder. To swing this large, heavy weapon so fast that it made a noise like thunder, it would have needed strong wing musculature. So it becomes clearly apparent why the Rodrigues Solitaire had a large keel on the sternum for the attachment of the wing muscles compared with that of the dodo. Also it explains why so many bones were fractured during fights.”

Some other bird species today have a similar knob-like structure or a different type of weapon in the wing, such as a spike, but there is nothing exactly like the musket ball of the Rodrigues Solitaire.

It’s estimated that there are around 5,000 solitaire fossils in collections around the world. However, there are only 7 almost complete skeletons, the most recent discovered by Dr Steel in Caverne L’Affouche on Rodrigues in May, 2013.

“Getting a true picture of what the bird looked like in life is still a bit of a challenge as there is no bird species left on Earth that is comparable. Very fortunately, there is a drawing of the bird, the only one known, which gives a good idea of what the Rodrigues Solitaire looked like in life,” Dr Hume said.

“As the Rodrigues Solitaire was the closest relative of the dodo, a bird we know practically nothing about, this research has also given a better understanding of the behavior in these birds, especially the dodo of which.”

“We can now say with some authority that the dodo was sexually dimorphic (different size in the sexes), but much less so than the Rodrigues Solitaire, was territorial, and defended its territory with its beak (and not with its wings as did the solitaire).”